Report on drugs, nonalkaloid organic nitrogenous bases     

T G Alexander 《Journal of the Association of Official Analytical Chemists》1974,57(2):258-260

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SCIENTIFIC MEN IN THE HALL OF FAME     

Alexander J 《Science (New York, N.Y.)》1941,93(2411):257

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Examination of sera from game birds for antibodies against avian viruses     

R E Gough  W J Cox  D J Alexander 《The Veterinary record》1990,127(5):110-111

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Bracken effects on inorganic nitrogen leaching from an upland podzol     

R. P. Smart    L. J. Calver    A. M. Crowe    K. M. Emmerson  & M. S. Cresser 《Soil Use and Management》2007,23(3):317-322

Leaching of inorganic N species to stream waters from upland areas of the UK is increasing, reflecting the increases in atmospheric deposition of nitrogen species due to increased levels of vehicular emissions. Bracken cover in UK uplands is also increasing overall ( Taylor, 1986 ), and the architectural nature of bracken has been shown to both increase deposition of atmospheric constituents to soils and change their chemical and physical nature. We have tested the nutrient status of upland podzols from the Lake District, Cumbria, UK, from under both moorland grass and bracken. The results show reduced levels of base cations and nitrate throughout the profile and decreases in the organic matter content of surface horizons as a consequence of bracken encroachment. We also report increased ammonium concentrations in lower soil horizons under bracken, possibly leading to increased leaching to stream waters. These results suggest either increased leaching of soil nutrients due to bracken encroachment or increased storage of nutrients within the bracken rhizome system. Results also suggest changes in either microbial activity or the microbial community of podzols, possibly due to the allelopathic nature of bracken. This may have caused changes in the soil nutrient dynamics, possibly accounting for some of the changes seen. We hypothesize that increased bracken cover within the British uplands has the potential to increase leaching of inorganic nitrogen to upland streams.  相似文献   

THE MOBILIZATION OF SCIENCE     

Alexander J 《Science (New York, N.Y.)》1943,97(2530):577-578

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Photosynthetic utilization efficiency of absorbed photosynthetically active radiation by Scots pine and birch forest stands in the southern Taiga     

Molchanov AG 《Tree physiology》2000,20(17):1137-1148

Absorption and utilization of photosynthetically active radiation (PAR) were investigated in Scots pine (Pinus sylvestris L.) and birch (Betula pendula Roth.) stands that were 41 years old at the end of the experimental period. Canopy depth of the Scots pine stand was about half that of the birch stand (6.5 versus 11.0 m), but absorption of PAR was similar in the two stands. The Scots pine forest canopy, with a leaf area index of 8.9, absorbed 90% of the incoming PAR (APAR), whereas the birch forest canopy, with a leaf area index of 5.9, absorbed 92% of APAR. During maximum foliage development, the upper Scots pine canopy absorbed more PAR than the upper birch canopy (75 versus 66%). The upper, middle and lower layers of the Scots pine canopy contained 37, 48 and 15% of the total needle surface area, respectively. The corresponding distribution of foliage surface area in the three layers of the birch canopy was 50, 30 and 20%, respectively. Measurements of photosynthetic rate were combined with estimates of leaf area index and stand phytomass to determine rates of primary production on a sunny day, a cloudy day, and on an annual basis. The energy equivalents of short- and long-term carbon gain were used with determinations of APAR to calculate photosynthetic utilization efficiency. Throughout the growing season, photosynthetic utilization efficiency of APAR in the upper canopy layer of the Scots pine forest was almost twice that in the lower canopy layer. In the birch forest, photosynthetic utilization efficiency was greater in the lower canopy layer than in the upper canopy layer. In all cases, utilization efficiency was higher in the birch stand than in the Scots pine stand (52 versus 29 J kJ(-1)). Taking account of respiration of the non-photosynthetic parts of each stand (night respiration of needles or leaves; respiration of branches, trunk and roots), estimated utilization efficiency of APAR for net primary production was 11 J kJ(-1) for Scots pine and 19 J kJ(-1) for birch. Solar conversion ratios, expressed as whole-plant net primary productivity per unit of APAR for the growing season, were 0.81 g MJ(-1) for Scots pine and 0.93 g MJ(-1) for birch.  相似文献   

Mechanical fuel treatment effects on fuel loads and indices of crown fire potential in a south central New Mexico dry mixed conifer forest     

Glenn J. Mason  Terrell T. Baker  Douglas S. Cram  Jon C. Boren  Alexander G. Fernald  Dawn M. VanLeeuwen 《Forest Ecology and Management》2007

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Aluminum fractions in root tips of slash pine and loblolly pine families differing in Al resistance     

Nowak J  Friend AL 《Tree physiology》2005,25(2):245-250

Aluminum (Al) distribution among several cellular fractions was investigated in root tips of seedlings of one Al-resistant and one Al-sensitive family of slash pine (Pinus elliottii Engelm.) and loblolly pine (Pinus taeda L.) grown in nutrient solution containing 100 microM AlCl3 (pH 4) for 167 h. Aluminum present in 5-mm-long root tips was fractionated into cell-wall-labile (desorbed in 0.5 mM citric acid), cell-wall-bound (retained after filtering disrupted cells through 20-microm mesh) and symplasmic (filtrate following cell disruption) fractions. When averaged across both species, 12% of Al absorbed by root tips appeared in the symplasmic fraction and 88% in the apoplasmic fraction (55% as cell-wall-labile, and 33% as cell-wall-bound). On a fresh mass basis, total Al in root tips was lower in loblolly pine than in slash pine, lower in the Al-resistant slash pine family than in the Al-sensitive slash pine family, and lower in the Al-resistant families than in the Al-sensitive families across species. Although the data support the hypothesis that Al-resistant plants limit Al uptake to root apices, they do not exclude other mechanisms of Al resistance. Differential Al resistance between the species and between slash pine families may also be associated with the size of the total non-labile and cell-wall-labile Al fractions, respectively. We were unable to identify the basis for differential Al resistance in loblolly pine.  相似文献   

Loss of hydraulic conductivity due to water stress in intact juveniles of Quercus rubra and Populus deltoides     

Tyree MT  Alexander J  Machado JL 《Tree physiology》1992,10(4):411-415

Despite many studies of the percent loss of hydraulic conductivity in excised branches, there is doubt as to whether cutting stems in air introduces unnatural embolism into the xylem at the cut surface. To address this question, hydraulic conductivity was measured in seedlings of northern red oak (Quercus rubra L.) and rooted scions of eastern cottonwood (Populus deltoides Bartr. ex Marsh.) that had been droughted in pots. Results indicate that in situ dehydration produced a very similar vulnerability curve (% loss of conductivity versus water potential) to those previously obtained by bench-top dehydration of excised branches of eastern cottonwood and red oak. In eastern cottonwood cuttings, conductivity loss increased sharply below water potentials of -1.0 MPa, with 100% loss of conductivity occurring by -2.0 MPa, whereas conductivity loss in red oak seedlings was more gradual, i.e., increasing below -1.5 MPa and sustaining 100% loss of conductivity by about -4.0 MPa.  相似文献   

Critical discussion of perpendicular to grain tension testing of structural timber – case study on the European hardwoods ash,beech and maple     

Philipp Schlotzhauer  Alexander Ehrmann  Susanne Bollmus  Holger Militz 《Wood material science & engineering》2020,15(5):278-288

ABSTRACT

Knowledge about perpendicular to grain tension behavior of wood is essential, since in construction tension stresses perpendicular to grain cannot be avoided completely. Especially for hardwoods, the data basis is scarce. EN 338 design values are with 0.6 N/mm² characteristic strength set very low. The US-American National Design Specifications even set this value to zero and make local reinforcements mandatory. This paper compares strength and stiffness values attained with newly-designed, little, prismatic specimens and EN 408 structural timber specimens to evaluate the current European design values. Little specimen’s characteristic strength values range from 7.2 to 10.6?N/mm² and are assumed to be real material properties. EN 408 specimen values are with approximately 4.0?N/mm² lower. These lower values are mainly due to stress peaks introduced by the force introduction. Strength values attained for the medium-dense European hardwoods beech, ash and maple exceed EN 338 design values by a factor of six to seven. Adaptation of the EN 338 design value is not recommended, though. The abundance of influencing factors makes clear that the design value and the ensuing design code have to be synchronized carefully by tedious testing in order to make use of the perpendicular to grain tension strength potential of the selected hardwoods.  相似文献